1. Field of the Invention
The invention relates to a motor-driven curtain assembly, more particularly to a motor control device that can provide overload protection to a motor of a motor-driven curtain assembly.
2. Description of the Related Art
Referring to FIG. 1, a conventional motor-driven curtain assembly 1 is shown to comprise a longitudinally extending hollow top rail 10, a longitudinally extending drive shaft 12 mounted rotatably in the top rail 10, a motor 15 for driving rotatably the drive shaft 12, a plurality of first hook members 11 mounted slidably on a bottom side portion of the top rail 10, a pair of second hook members 13 mounted threadedly on the drive shaft 12, a pair of curtain pieces 14, each of which has a top end that engages a respective set of the first hook members 11 and a respective one of the second hook members 13, pairs of first and second optical sensors 161, 162 mounted in the top rail 10 for limiting operation of the motor 15 during closing and opening movement of the curtain pieces 14, and a switch unit 17 for controlling operation of the motor 15.
In use, when a CLOSE key 171 on the switch unit 17 is operated, the motor 15 will be activated to drive the drive shaft 12 to rotate in a positive direction. The second hook members 13 are mounted respectively on externally threaded sections of the drive shaft 12 that are threaded in opposite directions. As such, rotation of the drive shaft 12 in the positive direction will result in axial translation of the second hook members 13 along the drive shaft 12 toward each other. Because each of the second hook members 13 is connected to the leading edge of a respective one of the curtain pieces 14, movement of the second hook members 13 toward each other will result in corresponding movement of the curtain pieces 14 toward each other to a closed position. When the second hook members 13 reach the vicinity of the first optical sensors 161, which are disposed at the intermediate portion of the top rail 10, the first optical sensors 161 will generate an inhibit signal for deactivating the motor 15, thereby completing the closing operation of the curtain assembly 1.
Accordingly, when an OPEN key 172 on the switch unit 17 is operated, the motor 15 will be activated to drive the drive shaft 12 to rotate in a negative direction opposite to the positive direction. Rotation of the drive shaft 12 in the negative direction will result in axial translation of the second hook members 13 along the drive shaft 12 away from each other, thereby moving the curtain pieces 14 away from each other to an open position. When the second hook members 13 reach the vicinity of the second optical sensors 162, which are respectively disposed adjacent to the opposite end portions of the top rail 10, the second optical sensors 162 will generate an inhibit signal for deactivating the motor 15, thereby completing the opening operation of the curtain assembly 1.
Some of the drawbacks of the aforesaid conventional curtain assembly 1 are as follows:
1. The motor 15 is deactivated only upon detection of the second hook members 13 by the first or second optical sensors 161, 162. When the motor 15 is activated to move the curtain pieces 14 to the closed position, and either of the curtain pieces 14 gets caught on an object such that the curtain pieces 14 are prevented from reaching the closed position, the motor 15 will keep operating in the activated state. In order to overcome the increase in load resistance, the amount of electric current flowing through the motor 15 will increase, thereby leading to possible damage to the motor 15 due to overload.
2. Two pairs of optical sensors 161, 162 are used to control deactivation of the motor 15. Installation of the curtain assembly 1 is relatively complicated due to the electrical connection between the optical sensors 161, 162 and the motor 15, which requires the consumer to possess a certain amount of technical skill in order to be able to make such connections.
Therefore, the object of the present invention is to provide a motor-driven curtain assembly having a motor control device that can provide overload protection to a motor of the curtain assembly and that dispenses with the use of optical sensors to simplify installation of the curtain assembly.
According to one aspect of the invention, a motor-driven curtain assembly comprises a longitudinally extending hollow top rail, a longitudinally extending drive shaft mounted rotatably in the top rail, a motor for driving rotatably the drive shaft, a curtain unit coupled to the drive shaft such that rotation of the drive shaft in a positive direction results in movement of the curtain unit to a closed position, and such that rotation of the drive shaft in a negative direction results in movement of the curtain unit to an open position, and a motor-control device that includes a driving circuit, a control unit, a current limiting circuit and an overload detector. The driving circuit is coupled to the motor for enabling rotation of the motor in the positive and negative directions. The control unit is coupled to the driving circuit and is operable so as to control the driving circuit to enable rotation of the motor in a selected one of the positive and negative directions. The current limiting circuit is adapted to couple the driving circuit to an external power source, and is adapted to limit current flow from the external power source to the driving circuit when the motor is subjected to an increase in load resistance. The overload detector, which is coupled to the control unit and the current limiting circuit, generates a control signal that is indicative of the amount of current flowing from the current limiting circuit to the driving circuit and that is provided to the control unit, thereby enabling the control unit to deactivate the driving circuit for stopping operation of the motor when overloading of the motor occurs.
According to another aspect of the invention, a motor-control device is adapted to be used in a motor-driven curtain assembly that includes a longitudinally extending hollow top rail, a longitudinally extending drive shaft mounted rotatably in the top rail, a motor for driving rotatably the drive shaft, and a curtain unit coupled to the drive shaft such that rotation of the drive shaft in a positive direction results in movement of the curtain unit to a closed position, and such that rotation of the drive shaft in a negative direction results in movement of the curtain unit to an open position. The motor-control device comprises:
a driving circuit adapted to be coupled to the motor and adapted to enable rotation of the motor in the positive and negative directions;
a control unit coupled to the driving circuit and operable so as to control the driving circuit to enable rotation of the motor in a selected one of the positive and negative directions;
a current limiting circuit adapted to couple the driving circuit to an external power source, and adapted to limit current flow from the external power source to the driving circuit when the motor is subjected to an increase in load resistance; and
an overload detector, coupled to the control unit and the current limiting circuit, for generating a control signal that is indicative of the amount of current flowing from the current limiting circuit to the driving circuit and that is provided to the control unit, thereby enabling the control unit to deactivate the driving circuit for stopping operation of the motor when overloading of the motor occurs.